Method of measuring the movement of an input device

ABSTRACT

A method of and an input device for measuring movement of an object ( 80 ) and the input device relative to each other, which movement comprises at least a scroll movement and a click movement, uses means ( 98,100,102 ) to determine the presence of the object on a window ( 78 ) of the input device. This allows measuring scroll movement and click movement with one sensor unit ( 92,94,96 ) of the input device and reduction of costs and size of the input device.

The invention relates to a method of measuring movement of an object anda user's input device relative to each other, which movement comprisesat least one a scroll movement or a click movement, whereby use is madeof an input device comprising at least one optical sensor unit, wherebythe measurement performed by the sensor unit comprises the steps ofilluminating an object surface with a measuring laser beam, capturingmeasuring beam radiation reflected by the object by a diode laser cavitythat emits the measuring beam and measuring changes in operation of thelaser caused by interference of the re-entering measuring beam radiationand the optical wave in the laser cavity. The invention also relates toan input device for carrying out the method and to an apparatuscomprising such an input device.

Such a method and user's input device (hereinafter input device) areknown from PCT patent application WO 02/37410. The optical input deviceof WO 03/37410 is intended to be used, for example, in a handheld orlaptop computer to move a cursor across a display, for example to selecta function of a displayed menu. To select a function, or item, from amenu, a human finger (the object) is moved in a direction across atransparent window in the housing of the input device. This movement iscalled a scroll action. The direction of the click movement may beperpendicular to the direction of the scroll movement, for example. Toactivate the selected function the finger is moved in a directionperpendicular to said window. This movement is called a click action.The input device may be small, because the optical sensor units can bemade very small. This opens the way to new applications for the inputdevice. For example, a user's input function can be built in a mobilephone for selecting items of a menu and for accessing Internet pages, inother hand-held apparatus or in a notebook computer.

The scroll-and-click input measuring method and device of WO 02/37410are substantially more reliable and simpler and cheaper than prior artmethods and devices. Use is made of a concept that is new for the typeof input devices discussed here. As will be explained herein after, thisconcept is a combination of Doppler shift a moving object, like a humanfinger, introduces in measuring laser beam and the so-called self-mixingeffect in a diode laser, which supplies the measuring beam. Self-mixingis the phenomenon that radiation emitted by a diode laser and, afterreflection from an object, re-entering the cavity of the diode laserinduces a variation in the gain of the diode laser and thus in theradiation emitted by the laser. The scroll-and-click method and deviceof WO 02/37410 allow measuring both the speed and direction of thescroll movement and detecting a click action by means of two diodelasers measuring paths (sensor units), which are, for example,orientated at opposite sharp angles relative to window of the device.This method will be referred to as the vector decomposition method. Thediode lasers may be supplied with periodically varying electricalcurrents and measuring signals generated during first and secondhalf-periods may be compared to determine the direction of the scrollaction.

It is an object of the invention to provide a new method of and a devicefor measuring scroll and click movement, which are even more simple andcompact and cheaper than those of WO 02/237410. The method ischaracterized in that use is made of only one optical sensor unit formeasuring a scroll movement and a click movement.

The new method is based on the insight that hitherto unused informationin the measuring beam of a sensor unit can be used to detect thepresence of a finger on the window of the input device. A single clickaction consists of a fast movement of the finger toward the devicewindow and back and a click action is preceded and succeeded by timeintervals wherein no movement takes place. Another possibility is: putthe finger on the window, retract the finger and put it gain on thewindow. Between the movement towards the window and the movement fromthe window, the finger is resting on the window for a short timeinterval. If such a resting, or presence on the window, of the finger isdetected, it can be concluded that a click action takes place. Thisdetection can be performed by the sensor unit which measures scrollmovement, so that a sensor unit and especially a diode laser can besaved. As the diode lasers are the most expensive components of theinput device, the new method is substantially cheaper than the methodwhich uses two sensor units, thus, two diode lasers. Saving one diodelaser, moreover, means reducing the space, which should be reserved inthe apparatus, which is provided with the capability to perform themethod.

A first embodiment of the method is characterized in that the presenceof an object on a window of the device is established by determiningwhether the re-entering measuring beam radiation comprises an amplitudecomponent which changes at lower frequencies than amplitude changescaused by a scroll movement.

In the input device of WO 02/37410 the high-frequency component of thesensor output signal is used for determining both a scroll and a clickaction. In the first embodiment of the present method use is made of theinsight that the low-frequency and DC portion of the output signalcomprise useable information about the presence of a finger on thewindow of the input device, and thus about a possible click action beingperformed.

The first embodiment may be further characterized in that the lowerfrequency component is measured by means of an additional detector.

Alternatively the first embodiment may be characterized in that thelower frequency component is separated from the sensor output signal.

A second embodiment of the method is characterized in that the presenceof an object on a window of the device is established by measuringvariation in an electrical current for driving the diode laser.

If a finger is present on the device window the diode laser forms partof a feedback loop, which is closed by a measuring photo diode arranged,for example, at the rear side of the diode laser, and the self-mixingeffect causes the efficiency of the laser to increase. This means thatthe laser drive current decreases when the finger is on the window.

A third embodiment of the method, wherein a periodically modulatedmeasuring beam is used, is characterized in that the presence of anobject on a window of the device is established by detecting presence ofa pattern of output signal undulations, in periods corresponding in timewith measuring beam pulse periods, which pattern is specific for thepresence of the object on the window of the device.

This embodiment uses the unique feature of an optical input deviceemploying the self-mixing effect that the presence of a finger on thewindow of the device causes a specific pattern of undulations in thesensor output signal. This specific pattern can be used to determine thepresence of a finger and, because a click action comprises tipping thefinger on and retracting it from the window, also whether a click actiontakes place. The periodically modulated measuring beam may be a pulsedmeasuring beam

The method using the undulations in the sensor output signal may becombined with the method, which uses the low frequency component in thissignal, to increase redundancy and reliability of the measurement.

There are several possibilities to measure the change in operation ofthe diode laser, which results in several embodiments of the method.

A first embodiment is characterized in that the measuring changes inoperation of the laser comprises measuring changes in the impedance ofthe laser.

The impedance of the diode laser is one of the parameters, which changedue to the interference effect and is a function of the relativemovement of the input device and the object or finger. This impedancecan be measured by measuring the voltage across the diode laser anddividing the measured voltage value by the known value of the electriccurrent sent through the diode laser.

A second and preferred embodiment of the method is characterized in thatmeasuring changes in operation of the laser comprises measuring changesin intensity of radiation emitted by the diode laser.

If radiation is coupled back to the laser cavity by a finger theintensity of the radiation emitted by the diode laser is increased whenthe laser drive current is kept constant.

The invention also relates to an input device for measuring movement ofan object and the input device relative to each other, which movementcomprises at least one scroll movement or a click movement, which inputdevice comprises at least one optical sensor unit, which comprises adiode laser having a laser cavity for supplying a measuring beam,optical means for converging the measuring beam at the object andmeasuring means for measuring changes in operation of the laser, whichchanges are due to interference of measuring beam radiation reflected bythe object and re-entering the laser cavity and the optical wave in thiscavity and for supplying an output signal that is dependent on movementof the object relative to the input device. This device is characterizedin that the optical sensor comprises additional means, which allowsestablishing presence of the object on a window of the device.

This input device makes an advantageous use of information availablefrom the sensor unit, which information has not been used before.

The sensor unit may use several types of additional means, either apartor in combination, which combination creates redundancy and increasesthe reliability of the obtained click movement information.

A first embodiment of the input device is, characterized in that theadditional means are constituted by means for a radiation-sensitivedetector arranged to receive measuring beam radiation and an electroniclow-pass filter, which provide a signal upon occurrence of a clickmovement.

Whereas in the device of WO 02/37410 for determining a click movementthe high frequency portion of the output signal of the sensor units isevaluated, in this embodiment of the device according to the inventionuse is made of the fact that the low frequency and DC componentcomprises useful information on the presence of a finger on the devicewindow and thus about a click movement.

A second embodiment of the input device is, characterized in that theadditional means are constituted by means for deriving a low-frequencycomponent from the output signal of the measuring means.

Information about click movement is now derived from the detector, forexample a monitor diode, which furnishes scroll information, instead offrom an additional radiation sensitive detector, so that a component canbe saved.

A third embodiment of the input device is characterized in that theadditional means are mans for measuring the drive current for the diodelaser.

In this embodiment use is made of the fact that the presence of a fingeron the input window will cause a reduction of the drive current for thediode laser. By measuring this current, the presence of a finger can beestablished and thus also whether a click movement takes place.

A fourth embodiment of the input device, wherein the sensor unit isactivated by activation pulses and the measuring means performmeasurements during time intervals determined by the activation pulses,is characterized in that the additional means comprise counting meansand comparing means to establish whether the number of undulations inthe output signal measuring during a first and second half of a saidtime interval are equal.

This embodiment uses the fact that whereas said numbers of undulationsin said first and second time interval half are different in case of ascroll movement, they are equal when the finger rests on the window.This will be temporally the case when a click motion is performed.

Also with respect to the sensor output signal, from which clickinformation may be derived according to the invention, differentembodiments are possible.

A first of these embodiments is characterized in that the measuringmeans are means for measuring a variation of the impedance of the lasercavity.

A second of these embodiments is characterized in that the measuringmeans is a radiation detector for measuring radiation emitted by thelaser.

Preferably, this embodiment is further characterized in that theradiation detector is arranged at the side of the laser cavity oppositethe side where the measuring beam is emitted.

Diode lasers are standard provided with a monitor diode at their rearside. Usually, such a monitor diode is used to stabilize the intensityof the laser beam emitted at the front side of the diode laser. Now themonitor diode is used to detect changes in the laser cavity, which aregenerated by radiation of the measuring beam re-entering the lasercavity.

In case measurement of an additional movement is required, the inputdevice may b characterized in that it comprises an additional opticalsensor unit for measuring an additional movement in a directiondifferent from the directions of the scroll movement and of the clickmovement.

The additional optical sensor may be used for measuring a second scrollmovement, for example perpendicular to the scroll movement mentionedherein above.

The input device may be used in different applications, such as inmobile phone, a cordless phone, a laptop or handheld computer, akeyboard for a desktop computer, a remote control unit, a write pen or avirtual pen.

These and other aspects of the invention are apparent from and will beelucidated, by way of non-limitative example, with reference to theembodiments described hereinafter. In the drawings:

FIG. 1 a shows, in cross-section, an embodiment of a known optical inputdevice, which uses the self-mixing effect and wherein the invention canbe implemented;

FIG. 1 b is a top view of this device;

FIG. 2 illustrates the principle of measuring by means of theself-mixing effect;

FIG. 3 shows the variation of the optical frequency and of the gain ofthe laser cavity as a function of the movement of the device and theobject relative to each other;

FIG. 4 illustrates a method of measuring this variation;

FIG. 5 shows the variation of laser wavelength as a function of thetemperature of a laser;

FIG. 6 shows the effect of the use of a periodically varying drivecurrent for a laser;

FIG. 7 illustrates how the direction of movement is detected;

FIGS. 8 and 9 show an embodiment of a known scroll-and-click device;

FIG. 10 shows a first embodiment of a scroll-and-click device accordingto the invention;

FIG. 11 shows a portion of a second embodiment of a scroll-and-clickdevice according to the invention;

FIG. 12 shows a cordless phone equipped with an input device wherein theinvention may be implemented;

FIG. 13 shows a TV set comprising a remote control equipped with such aninput device;

FIG. 14 shows a laptop computer equipped with such an input device;

FIG. 15 shows a desktop computer equipped with such an input device;

FIG. 16 shows a pen equipped with such an input device, and

FIG. 17 shows a virtual pen equipped with such an input device.

FIG. 1 a is a diagrammatic cross-section of an embodiment of the knownoptical input device. The device comprises at its lower side a baseplate 1, which is a carrier for the diode lasers, in this embodimentlasers of the type VCSEL, and the detectors, for example photo diodes.In FIG. 1 a only one diode laser 3 and its associated photo diode 4 isvisible, but usually at least a second diode laser 5 and associateddetector 6 is provided on the base plate, as shown in the FIG. 1 b topview of the apparatus. The combination of a diode laser, its associatedphotodiode and a lens is referred to as a sensor unit. The diode lasers3 and 5 emit laser, or measuring, beams 13 and 17, respectively At itsupper side the device is provided with a transparent window 12 acrosswhich an object 15, for example a human finger is to be moved. A lens10, for example a plane-convex lens is arranged between the diode lasersand the window. This lens focuses the measuring beams 13 and 17 at ornear the upper side of the transparent window.

If an object 15, for example a human finger, is present at thisposition, it scatters the beam 13. A portion of the radiation of beam 13is scattered in the direction of the measuring beam 13 and this portionis converged by the lens 10 on the emitting surface of the diode laser 3and re-enters the cavity of this laser. As will be explainedhereinafter, the radiation returning in the cavity induces changes inthis cavity, which results in, inter alia, a change of the intensity ofthe laser radiation emitted by the diode laser. This change can bedetected by the photo diode 4, which converts the radiation variationinto an electric signal, and an electronic circuitry 18 for processingthis signal. The measuring beam 17 is also focused on the object,scattered thereby and part of the scattered radiation re-enters thecavity of the diode laser 5. The circuitry 18 and 19, for the signal ofthe photo diode 6, shown in FIGS. 1 a and 1 b has only an illustrativepurpose and may be more or less conventional. As is illustrated in FIG.1 b, this circuitry is interconnected.

FIG. 2 illustrates the principle of movement measurement by means of theself-mixing effect. In this Fig., the diode laser, for example diodelaser 3, is schematically represented by its cavity 20 whilst its frontand rear facets are represented by laser mirrors, 21 and 22,respectively. The cavity has a length L. The object, whose movement isto be measured, is denoted by reference numeral 15. The space betweenthis object and the front facet 21 forms an external cavity, which has alength L₀. The laser beam emitted through the front facet is denoted bythe reference numeral 25 and the radiation reflected by the object inthe direction of the front facet is denoted by reference numeral 26.Part of the radiation generated in the laser cavity passes through therear facet and is captured by the photo diode 4.

If the object 15 moves in the direction of the measuring beam 25, thereflected radiation 26 undergoes a Doppler shift. This means that thefrequency of this radiation changes or that a frequency shift occurs.This frequency shift is dependent on the velocity with which the objectmoves and is of the order of a few kHz to MHz. The frequency-shiftedradiation re-entering the laser cavity interferes with the optical wave,or radiation generated in this cavity, i.e. a self-mixing effect occursin the cavity. Dependent on the amount of phase shift between theoptical wave and the radiation re-entering the cavity, this interferencewill be constructive or negative, i.e. the intensity of the emittedlaser radiation is increased or decreased periodically. The frequency ofthe laser radiation modulation generated in this way is exactly equal tothe difference between the frequency of the radiation generated in thecavity and that of Doppler-shifted radiation re-entering the cavity. Thefrequency difference is of the order of a few kHz to MHz and thus easyto detect. The combination of the self-mixing effect and the Dopplershift causes a variation in the behavior of the laser cavity; especiallyits gain, or light amplification, varies.

This is illustrated in FIG. 3. In this Fig., curves 31 and 32 representthe variation of the frequency ν of the emitted laser radiation and thevariation of the gain g of the diode laser, respectively, as a functionof the distance L₀ between the object 15 and the front mirror 21. Bothν, g and L₀ are in arbitrary units. As the variation of the distance L₀is the result of movement of the object, the abscissa of FIG. 3 can bere-scaled in a time axis, so that the gain will be plotted as a functionof time. The gain variation Δg as a function of the velocity v of theobject is given by:${\Delta\quad g} = {\frac{- K}{L} \cdot \cos \cdot \left\{ {\frac{4{\pi \cdot \upsilon \cdot v \cdot t}}{c} + \frac{4{\pi \cdot L_{0} \cdot t}}{c}} \right\}}$In this equation:

-   -   K is the coupling coefficient to the external cavity; it is        indicative of the quantity of radiation coupled out of the laser        cavity;    -   ν is the frequency of the laser radiation;    -   v is the speed of the object in the direction of the measuring        beam    -   t denotes time, and    -   c is the light velocity.

The object surface is moved in its own plane, as is indicated by thearrow 16 in FIG. 2. Because the Doppler shift occurs only for an objectmovement in the direction of the beam, this movement 16 should be suchthat it has a component 16′ in this direction. Thereby, it becomespossible to measure a movement in an XZ plane, i.e. the plane of drawingof FIG. 2 which movement can be called the X movement. FIG. 2 shows thatthe object surface has a skew position with respect to the rest of thesystem. In practice, usually the measuring beam is a skew beam and themovement of the object surface will take place in an XY-plane. TheY-direction is perpendicular to the plane of the drawing in FIG. 2. Themovement in this direction can be measured by a second measuring beam,emitted by a second diode laser, and scattered light of which iscaptured by a second photo diode associated with the second diode laser.A (the) skew illumination beam(s) is (are) obtained by arranging thediode laser(s) eccentrically with respect to the lens 10, as shown inFIG. 1.

Measuring the variation of the laser cavity gain caused by the objectmovement by measuring the intensity of the radiation at the rear laserfacet by a monitor diode is the simplest, and thus the most attractiveway. Conventionally, this diode is used for keeping the intensity of thelaser radiation constant, but now it is used for measuring the movementof the object.

Another method of measuring the gain variation, and thus the movement ofthe object, makes use of the fact that the intensity of the laserradiation is proportional to the number of electrons in the conductionband in the junction of the laser. This number in turn is inverselyproportional to the resistance of the junction. By measuring thisresistance, the movement of the object can be determined. An embodimentof this measuring method is illustrated in FIG. 4. In this Figure, theactive layer of the diode laser is denoted by the reference numeral 35and the current source for supplying this laser is denoted by referencenumeral 36. The voltage across the diode laser is supplied to anelectronic circuit 40 via a capacitor 38. This voltage, which isnormalized with the current through the laser, is proportional to theresistance, or impedance, of the laser cavity. The inductance 37 inseries with the diode laser forms high impedance for the signal acrossthe diode laser.

Besides the amount of movement, i.e. the distance across which theobject is moved and which can be measured by integrating the measuredvelocity with respect to time, also the direction of movement has to bedetected. This means that it has to be determined whether the objectmoves forward or backward along an axis of movement. A first method todetermine the direction of movement uses the shape of the signalresulting from the self-mixing effect. As shown by graph 32 in FIG. 3,this signal is an asymmetric signal. The graph 32 represents thesituation where the object 15 is moving towards the laser. The risingslope 32′ is steeper than the falling slope 32″. The asymmetry isreversed for a movement of the object away from the laser, i.e. thefalling slope is steeper than the rising slope. By determining the typeof asymmetry of the self-mixing signal, the direction of movement of theobject can be ascertained.

Under certain circumstances, for example for a smaller reflectioncoefficient of the object or a larger distance between the object andthe diode laser, it may become difficult to determine the shape orasymmetry of the self-mixing signal. Therefor, a second method ofdetermining the direction of movement is preferred. The second methoduses the fact that the wavelength λ of the laser radiation is dependenton the temperature of, and thus the current through, the diode laser.If, for example, the temperature of the diode laser increases, thelength of the laser cavity increases and the wavelength of the radiationthat is amplified increases. Curve 45 of FIG. 5 shows the temperature(T_(d)) dependency of the wavelength λ of the emitted radiation. In thisFigure, both the horizontal axis, T_(d), and the vertical axis, λ, arein arbitrary units.

If, as is shown in FIG. 6, a periodic drive current I_(d), representedby the graph 50, is supplied to the diode laser, the temperature T_(d)of the diode laser rises and falls periodically, as shown in graph 52.This results in a standing optical wave in the laser cavity which has aperiodically varying frequency and thus a continuously varying phaseshift with respect to the radiation reflected by the object andre-entering the cavity with a certain time delay. In every half periodof the drive current, there are now successive time segments wherein thediode laser gain is alternately higher and lower, depending on the phaserelation of the wave in the cavity and the reflected radiationre-entering the cavity. This results in a time-dependent intensityvariation (I), or undulations, of the emitted radiation as shown ingraph 54 of FIG. 6. This graph represents the situation for astationary, or non-moving, object. The number of undulations in a firsthalf period ½p(a) is equal to the number of undulations in a second halfperiod ½p(b).

A movement of the object causes a Doppler shift of the radiationre-entering the laser cavity, i.e. this frequency increases or decreasesdependent on the direction of movement. A movement of the object in onedirection, the forward direction, causes a decrease of the wavelength ofthe re-entering radiation, and a movement in the opposite directioncauses an increase in the wavelength of this radiation. The effect theperiodic frequency modulation of the optical wave in the laser cavityhas in case of a Doppler shift depends on the sign of the Doppler shifthas relative to the sign of the frequency modulation in the lasercavity. If the two frequency shifts have the same sign, the phasedifference between the optical wave and the re-entering radiationchanges at a slow rate, and the frequency of the resulting modulation ofthe laser radiation is lower. If the two frequency shifts have oppositesigns, the phase difference between the optical wave and the radiationchanges at a faster rate, and the frequency of the resulting modulationof the laser radiation is higher. During a first half period, ½p(a), ofthe laser driving current, the wavelength of the generated laserradiation increases. In case of a backward moving object, the wavelengthof the re-entering radiation also increases, so that the differencebetween the frequencies of the optical wave in the cavity and that ofthe radiation re-entering this cavity is lower. Thus the number of timesegments during which the wavelength of re-entering radiation is adaptedto the wavelength of the generated radiation is smaller than in the caseof absence of electrical modulation of the emitted laser radiation. Thismeans that, if the object moves in the backward direction, the number ofundulations in the first half period is smaller than if no modulationwould be applied. In the second half period, ½p(b), wherein the lasertemperature and the wavelength of the generated radiation decrease, thenumber of time segments wherein the wavelength of the re-enteringradiation is adapted to that of the generated radiation increases. Thus,for a backward moving object, the number of undulations in the firsthalf period is smaller than the number of undulations in the second halfperiod. This is illustrated in graph 58 of FIG. 7, which graph shows theintensity I_(b) of the laser radiation emitted if the object moves inthe backward direction. Comparing this graph with graph 54 of FIG. 6learns that the number of undulations in the first half period hasdecreased and the number of undulations in the second half period hasincreased.

It will be clear from the above explanation that if the object moves inthe forward direction, in which the wavelength of radiation scattered bythe object and re-entering the laser cavity decreases due to the Dopplereffect, the number of undulations in a first half period ½p(a) is largerthan the number of undulations in a second half period ½p(b). This canbe verified by comparing graph 56 of FIG. 7, representing the intensityI_(f) of the radiation emitted in the case of a forward moving object.In an electronic processing circuit, the number of photo diode signalundulations counted during the second half period ½p(b) is subtractedfrom the number of undulations counted during the first half periods½p(a). If the resulting signal is zero, the object is stationary. If theresulting signal is positive, the object moves in the forward directionand if this signal is negative, the object moves in the backwarddirection.

Instead of the triangular shaped drive current I_(d) used in theembodiment described with reference to FIGS. 5 and 6, also a drivecurrent of another shape, such as a sinusoidal or rectangular shape, maybe used.

The method of measuring the velocity and the direction of the objectmovement described above can also be used if the gain variation isdetermined by measuring the variation of the resistance of the diodelaser cavity.

The measuring method requires only a small Doppler shift, for example interms of wavelength, a shift of the order of 1,5.10⁻¹⁶ m, whichcorresponds to a Doppler frequency shift of the order of 100 kHz for alaser wavelength of 680 nm.

As hardly any requirements have to be set to the structure or reflectioncoefficient of the object surface many types of objects can be used toactivate the input device. For example, it has been demonstrated thatalso movement of a piece of paper can be measured with the device.

From an optical point of view, the dimensions of the optical inputdevice, which uses the self-mixing effect is already small. The size ofthis device, when implemented as a module is mainly determined by theamount of electronics that has to be incorporated in the module and bythe aspect of easy manufacturing. For example the window of such amodule has a diameter of 3-5 mm. Because of the measuring principle usedin this device, its components need not to be aligned accurately, whichis great advantage for mass production. By using the present invention adiode laser, which is the most expensive component of the device, can besaved, so that the price and size of the device van be decreased andmanufacture becomes easier.

In FIG. 8 an embodiment of an optical scroll-and-click input device 60,which is known from WO 02/37410, is shown to compare it with such adevice according to the invention, shown in FIG. 10. The device of FIG.8 comprises two optical sensor units 62,64, each of which may comprise adiode laser and photodiode assembly 66,68. Instead of such an assembly,also separate diode lasers and photo diodes may be used. In each of thepaths of the radiation emitted by the units 62,64 a lens 70, 72 isarranged, which focuses radiation beams 74,76 of the associated units62,64 substantially in an action plane 88, which may be the plane of awindow. This window 78 may form part of the housing 82 of the apparatusin which the device is used, for example a mobile phone as shown in FIG.10. The sensor units may be arranged such that the chief rays of themeasuring beams 74,76 are at opposite angles with respect to the normalto the window 82, for example at angles of +45° and −45°, respectively.

An object, for example a human finger 80 is moved across the actionplane for a scrolling and/or clicking action. As described herein above,both actions cause a Doppler shift in the radiation reflected by thefinger towards the laser/diode assemblies units 66, 68. The outputsignals of the detectors of these units are supplied to signalprocessing and laser drive electronic circuitry 64. This circuitryevaluates the movements of, for example the controlling finger 80 andsupplies information about these movements at its output 86. The sensorunits 62,64, the window 88 and the electronic circuitry 84 and softwaremay be integrated in one module. This module is placed as such in themobile phone or in another apparatus, which should be provided with ascrolling and clicking function. It is also possible to implement theinput device with discrete elements. Especially part of the signalprocessing may be carried out by a micro controller or other controllingmeans which forms part of the mobile phone or other apparatus, such as aremote control, a cordless phone or a portable computer.

As described herein before the velocity and direction of a fingermovement with respect to the sensor units may be detected by modulatingthe laser currents and counting the radiation pulses received by thedetectors. From the output signals Sign₁ and Sign₂ of these detectors,which represent velocities of the object along the chief rays of themeasuring beams 74,76, the velocity (V_(scroll)) parallel to the windowand the velocity (V_(click)) perpendicular to the window can, for theplus and minus 45° orientation of the measuring beams of FIG. 8, becalculated as follows:V _(scroll)=½{square root}2.(Sign₁−Sign₂)V _(click)=½{square root}2.(Sign₁+Sign₂)

The scroll and click movements are thus determined by means of a vectortransform of all available directional information, i.e. the signals ofall detectors present in the input device.

According to the invention hitherto unused information can be employedto determine the presence of a finger on the window of the device andthus whether a click movement is performed. As this information is of adifferent nature than scroll movement information, it can be obtainedfrom the sensor unit, which provides information about a scrollmovement. This means that a scroll movement and a click movement can bedetermined by means of only one sensor unit.

FIG. 10 shows an embodiment of an input device 90 according to theinvention, used in a mobile phone apparatus 82. The single sensor unitcomprises a diode laser and photo diode (monitor diode) assembly 92 anda lens 94 to converge the measuring beam from the diode laser on thewindow 78 of the input device. The monitor diode is coupled to anelectronic circuit 98, which processes the monitor output signal andcontrols the laser drive current. Reference number 100 denotes theoutput of this circuit or an interface to control functions of theapparatus outside the input device, like mobile phone menus. As thechief ray of the measuring beam is incident at a sharp angle on thewindow, it has a component in both the scroll direction X and the clickdirection Z. A scroll movement and a click movement will both cause achange in the measuring beam radiation reflected back in the diode lasercavity. To determine whether it is a scroll movement or a click movementthat causes such a change, it is established whether the finger isresting or has rested on the window during a given time duration. Ifthis is the case, it can be concluded that a click action is performed.For, such an action consist of a fast movement in the Z-direction of thefinger toward the window, a window touch of the finger and a fastretracting of the finger from the window.

As remarked herein above, the frequency of the laser radiationmodulation, which is due to movement of the finger across the window isin the order of a few kHz to MHz. It has found that in case the fingerrests on the window, the laser radiation will also have an amplitudecomponent which varies at a substantially lower frequency, for examplelower than 1 kHz. The presence of such a low-frequency component can bedetected by means of an additional detector (photo diode), denoted by102 in FIG. 10, which is arranged such that it receives a portion of themodulated radiation. The amount of radiation incident on the photo diode102 may be controlled by arranging a beam splitter (not shown), forexample a partially reflecting mirror, in the path of the measuringbeam. This beam splitter reflects a fixed portion of the measuring beamradiation towards the additional photo diode. The additional photo diodeis coupled to the laser drive and signal processing circuit 100. Thiscircuit can thus establish whether a click action does occur or not,thus whether the measured movement is a click movement or a scrollmovement.

The occurrence of the low frequency radiation modulation can also bedetected by means of the monitor diode, as shown in FIG. 11. This Figureshows the assembly 92 comprising the diode laser 104 and the monitordiode 106 for receiving laser radiation 97 emitted at the rear side ofthe diode laser. Part of the monitor diode signal S_(d) is supplied to alow pass filter 108 that passes only the low-frequency component S_(l)to the signal processing circuit 98. The rest of the signal S_(d) issupplied directly as signal S_(h) to the circuit 98.

Again, in this circuit it is established whether a click movement occursor not, i.e. whether a low frequency signal component is present or not,thus whether the measured movement, i.e. the information of S_(h), is aclick movement or a scroll movement. It is also possible to supply thewhole signal S_(d) to the circuit 98 and that this circuit isolates thelow frequency component from the signal S_(d).

During the time that a finger rests on the window an opto-electronicfeedback loop exists, which loop encompasses the diode laser and thedevice window, between which elements measuring beam radiationpropagates forth and back, the monitor diode and the laser drivecircuit. The effect of coupling back laser radiation in the cavity isthat the same amount of radiation is emitted at smaller laser driveelectrical current. When a finger is present on the device window thedrive current decreases, so that such a presence can be established bymeasuring this drive current, for example in the circuit of FIG. 4 or asimilar circuit well known to a person skilled in the art. The result ofsuch a measurement allows determining whether the movement measured withthe monitor diode is a click movement or a scroll movement.

In case a pulsed laser diode laser is used, the presence of a finger onthe device window can also be established by means of counting thenumber of undulations in the detector signal occurring in the first andsecond half of a laser drive current period. As explained at the hand ofFIGS. 6 and 7, the number of undulations in a first half period will beequal to the number of pulses in the second half period if the finger isstationary on the window. In case of a scroll movement these numberswill be unequal. By counting the number of undulations during said halfperiods and comparing these numbers with each other it can be determinedunambiguously whether the finger rests, or has rested on the window.Thus it can be established whether the measured variations in the lasercavity are due to a click movement or to a scroll movement.

Each of the four embodiments of the new method may be combined with oneor more of the other embodiments to obtain redundancy and thus toincrease the reliability of the measurement. Each of these embodimentsmay also be used in combination with one the methods of measuring thevariations in the laser cavity due to the self-mixing effect and theDoppler shift.

Also in an input device for measuring movement of an object in threedirections, for example X- and Y-scroll and click, using a separatesensor unit for each of the directions and described in WO 02/37410, onesensor unit can be saved when using the present method. An input devicesimilar to that shown in FIGS. 1 a, 1 b or similar to that shown FIGS.8,9 is then obtained, whereby the chief rays of the measuring beams ofthe sensor units are oriented such that movements in the X-, Y- and Zdirection can be measured. The new method can be used for the two sensorunits, so that redundancy is created and reliability increased. Saving asensor unit, especially a diode laser and photodiode assembly may be ofgreat importance in practice, because a diode laser is the most costlycomponent of the input device. Moreover, saving a sensor unit means thatthe device can be made more compact and that it becomes easier built-inthe device in the envisaged apparatus. It is also possible to use thenew method with an input device having the original number of sensorunits, for example three. One of the sensor units can be used formeasuring a scroll movement in the X direction and a click movement, thesecond sensor unit can be used for measuring scroll movement in the Ydirection and the third sensor unit is available to produce additionalinformation.

With respect to the design aspect, other embodiments of the opticalinput device than those shown in FIGS. 1 a, 1 b and in FIGS. 8, 9 arepossible, similar to the embodiments described in WO 02/37410. Forexample, between the diode laser(s) and the window (an) optical fiber(s)may be arranged to guide radiation from the diode laser to the to windowand back. Thereby flexibility in design is obtained and the distancebetween the diode laser and the window can be enlarged, which allowsarranging components of the input device those positions in theapparatus, where space is available. The input device is then no longerone module, as is the input device of FIGS. 1 a, 1 b.

Previous European patent application having filing number 02077217.4(PHNL020523) describes a new and inventive method of processing theoutput signals of the sensor units. This method allows an unambiguousdiscrimination between a scroll movement and a click movement and a veryreliable detection of the direction (upward or downward) of a scrollmovement. In said method no longer use is made of vector decomposition.Its characteristic features are that scroll movement information andclick movement information are derived from the same sensor(s) signaland that analyzing the sensor(s) signal comprises determining whethersuch a signal shows a first time pattern, which is typical for a clickmovement, or a second time pattern, which is typical for a scrollaction, which first time pattern is different from the second timepattern.

Thereby use is made of the fact that a user will never scroll and clickat the same time and of the insight that a click movement generates asensor unit output signal that is substantially different from such anoutput signal generated by a scroll movement. The click action is afast, short duration, movement, which is preceded and succeeded by aperiod of non-movement and thus generates a burst like responsecomprising one or more pulses during a short time interval. Thisspecific signal shape is independent of the individual user's fingermotorization and the direction of the click (up-click or down-click). Ascroll action generates, during the same time period, a considerablylarger number of signal undulations having lower peaks than the singleburst generated by a click action.

Preferably for analysis of a sensor signal obtained during a given timeinterval use is made of movement data obtained during other timeintervals. Taking past and future measurements into account whenanalyzing a signal measured during a given, intermediate, time intervalallows very reliably determining the direction of a scroll action, i.e.an upward scroll or a downward scroll. Delaying in time the analysis ofsignals obtained during the said given time interval allows using saidfuture measurements, i.e. measurements done after the said given timeinterval.

An embodiment of the present method of detecting the presence of afinger, or another object, on the input device window includes thecombination of this present method with the method according to theprevious EP application having filing number 02077217.4. Thiscombination provides the advantage that, by combining data obtained bymeans of the two methods the final measuring results are very reliable.For details about the processing of the different signals generated by ascroll action and a click action using the difference in time patternsof these signals and for embodiments of algorithms to perform thisprocessing, reference is made to the previous EP application, which isincorporated herein by reference.

An input device wherein the invention is implemented may not only beused in a mobile, or cellular, phone apparatus, but also in otherapparatus of different types, some of which will be discussed briefly.

FIG. 12 shows a cordless phone apparatus 110 provided with an inputdevice wherein the invention is implemented. This apparatus is composedof a base station 112, which is connected to a phone or cable networkand the movable apparatus 124 which can be used within an area with aradius of, for example, less than 100 m from the base station. Apparatus114 comprises a keyboard section 115 and a display device 117. In asimilar way as described for the mobile phone apparatus, the apparatus114 is provided with a user's input device 119 as discussed hereinabove. In FIG. 12 only the window of the optical input device is shown.Preferably, in this and the other applications, the window has a convexshape so that the user can easily find the device position, even in poorlighting conditions. Moreover the window is then kept clear by means offinger movements, which wipe dust and grease from the window.

FIG. 13 shows a remote control unit 130 for use with a conventional TVset 120, which comprises a receiver and display apparatus 122 and a settop box 128 to make the apparatus suitable for, for example, Internetcommunication. This box provides access to the Internet via a phone orcable network, and converts the signal received from the Internet into asignal that can be processed by the TV set in order to display theInternet information. As a user of the TV Internet should have the inputdevice for Internet commands at hand, this input device 134 should beintegrated in the remote control unit. The input device 134, wherein theinvention may be implemented and of which FIG. 13 shows only the window,may be arranged between the conventional buttons 132 of the remotecontrol unit or at any other position within reach of any of the humanfingers holding the remote control unit.

An input device wherein the invention is implemented may also be used ina computer configuration to replace a conventional hand-driventrack-ball mouse or a mouse pad. FIG. 14 shows a portable computer 140,which is known as notebook or laptop, comprising a base portion 142 anda cover portion 146 with a LCD display 148. The base portionaccommodates the different computer modules and the keyboard 144. Inthis keyboard, an optical input device 150 as described herein above isarranged which replaces the conventional mouse pad. The input device maybe arranged at the position of the conventional mouse pad or at anyother easily accessible position.

A hand-held, for example palmtop, computer is a smaller version of thenotebook. Also such a hand-held computer may be provided with an opticalinput device wherein the invention is implemented, for example toreplace a pen for touching the display screen, which pen is usuallyapplied to select a function of a displayed menu. The input device maybe arranged in the keyboard of the hand-held computer, but also at theinner side of the cover. A personal digital assistant (PDA) may beconsidered as a type of hand-held computer so that a PDA or a gamecomputer may also be provided with an input device wherein the inventionis implemented.

FIG. 15 shows a desktop computer configuration 160 wherein an opticalinput device can be applied in several ways to replace the conventionaltrackball mouse. The computer configuration is composed of a keyboard162, a computer box 164 and a monitor 166. The monitor may be a flat LCDmonitor fixed in a support 168, as shown in the Figure, or a CRTmonitor. An optical input device 170 as described herein above isintegrated in the keyboard so that a separate mouse and its cable to thecomputer box are no longer needed.

In the computer configurations described above, the input device may bearranged in the display portion, instead of in the keyboard portion, forexample in the cover 146 of the laptop computer of FIG. 14 or in thecover of a hand-held computer. The input device may also be incorporatedin displays other than computer displays.

The optical input device may also be incorporated in a normal pen or ina virtual pen to measure the movements of such a pen. In theseapplications fibers may be used to guide radiation from the diode lasersto the window of the device, so that the main part of the device can bearranged at a position remote from the pen point.

FIG. 16 shows a normal pen 180 having a penholder 181 and a pen point182. A sleeve-shaped housing 186 for the components of the input deviceis fixed on the penholder end opposite the pen point. The housing 186accommodates the diode lasers, the photo diodes and the electroniccircuitry of the input device. Optical fibers 183,184 guide theradiation from the diode lasers. These fibers end, for example, halfwaythe pen point and their front ends form the window of the input device.It is also possible to arrange the diode lasers and the photo diodes ata position remote from the pen and to transmit the radiation from thediode lasers to the pen point and back to the diode lasers via externaloptical fibers, the front ends of which are fixed to the pen point.

When the pen is moved for writing a text or making a drawing, themovement is measured by the input device and converted into anelectrical signal. This signal is, for example, immediately transmittedto a computer via a wire 188 or wirelessly. The computer processes thissignal so that the written text or the drawing can be made visible,immediately or after some time, on the computer display or sent toanother computer or archive. The input device of the pen can also beused for measuring a scroll movement or a click movement so that the pencan be used as a computer mouse. A click action can be used foractivating the input device of the pen or for choosing another item orfunction of the pen menu. The pen can also be used in combination with amobile phone whereby the mobile phone can be used to transmit the textor drawing to a remote location. The pen may also be provided with meansfor temporally storing the text or graphics produced by the user.

FIG. 17 shows a vertical cross-section of a virtual pen. Such a pen ismoved across featureless paper or another underground according to arequired pattern, which may be letters, words, drawings etc. Thispattern is translated via the input device of the pen to into positions.A computer program, present in for example a computer or a mobile phone,can translate these positions into a virtual text or drawing. Thevirtual pattern can be converted into a visual pattern and displayed,immediately or later on, by this computer or sent to another computer orinto a network.

The embodiment of the virtual pen 190 shown in FIG. 17 comprises a penhouse 191 with a pen point 192, a base plate 193 at the lower side and atransparent window 194 in the pen point. The lower side of the penaccommodates, for example, two diode lasers 3, 4 and the associatedphoto diodes and signal processing and laser drive circuitry diode.These components may be mounted on a layer 195. Optical fibers 196, 197are coupled to the diode lasers to guide the laser radiation to thewindow 194. Jacket or sleeves 198, 199 of solid material, for example,plastics fix these fibers.

1. A method of measuring movement of an object and a user's input devicerelative to each other, which movement comprises at least one scrollmovement or a click movement, whereby use is made of an input devicecomprising at least one optical sensor unit, whereby the measurementperformed by the sensor unit comprises the steps of illuminating anobject surface with a measuring laser beam, capturing measuring beamradiation reflected by the object by the diode laser cavity that emitsthe measuring beam and measuring changes in operation of the lasercaused by interference of the re-entering measuring beam radiation andthe optical wave in the laser cavity, characterized that one sensor unitis used to measure both a scroll motion and a click motion.
 2. A methodas claimed in claim 1, characterized in that the presence of an objecton a window of the device is established by determining whether there-entering measuring beam radiation comprises an amplitude componentwhich changes at lower frequencies than amplitude changes caused by ascroll movement.
 3. A method as claimed in claim 2, characterized inthat the lower frequency component is measured by means of an additionaldetector.
 4. A method as claimed in claim 2, characterized in that thelower frequency component is separated from the sensor output signal. 5.A method as claimed in claim 1, characterized in that the presence of anobject on the window of the device is established by measuring avariation in an electrical current for driving the diode laser.
 6. Amethod as claimed in claim 1, wherein a periodically modulated measuringbeam is used, characterized in that the presence of an object on awindow of the device is established by detecting presence of a patternof output signal undulations in periods corresponding in time withmeasuring beam pulse periods, which pattern is specific for the presenceof the object on the window.
 7. A method as claimed in claim 1,characterized in that, moreover, scroll movement information and clickmovement information are derived from the same sensor unit(s) outputsignal and it is determined whether the output signal shows a first timepattern, which is typical for a click movement, or a second timepattern, which is typical for a scroll movement, which first timepattern is different from the second time pattern.
 8. A method asclaimed in claim 7, characterized in that for analyzing an output signalobtained during a time interval use is made of movement date obtainedduring other time intervals.
 9. A method as claimed in claim 1,characterized in that measuring changes in operation of the lasercomprises measuring changes in the impedance of the diode laser.
 10. Amethod as claimed in claim 1, characterized in that measuring changes inoperation of the laser comprises measuring changes in the intensity ofthe radiation emitted by this cavity.
 11. An input device for measuringmovement of an object and the input device relative to each other, whichmovement comprises at least one scroll movement or a click movement,which input device comprises at least one optical sensor unit, whichcomprises a diode laser having a laser cavity for supplying a measuringbeam, optical means for converging the measuring beam at the object andmeasuring means for measuring changes in operation of the laser, whichchanges are due to interference of measuring beam radiation reflected bythe object and re-entering the laser cavity and the optical wave in thiscavity and for supplying an output signal that is dependent on movementof the object relative to the input device, characterized in that theoptical sensor comprises additional means, which allows establishingpresence of the object on a window of the device.
 12. An input device asclaimed in claim 11, characterized in that the additional means areconstituted by means for establishing whether the modulated measuringbeam radiation comprises a component having lower frequencies than thosecaused by a scroll movement.
 13. An input device as claimed in claim 12,wherein the sensor unit comprises a first radiation-sensitive detectorfor measuring variations in the laser cavity, characterized in that theadditional means is constituted by a second radiation-sensitive detectorarranged for receiving measuring beam radiation, which is non-incidenton the laser cavity.
 14. An input device as claimed in claim 12,characterized in that the additional means are constituted by electronicmeans for detecting said component in the output signal of the measuringmeans.
 15. An input device as claimed in claim 11, characterized in thatthe additional means are mans for measuring the drive current for thediode laser.
 16. An input device as claimed in claim 11, wherein thesensor unit is activated by activation pulses and the measuring meansperform measurements during time intervals determined by the activationpulses, characterized in that the additional means comprises countingmeans and comparing means to establish whether the number of undulationsin the output signal measured during a first and second half of a saidtime interval are equal.
 17. An input device as claimed in claim 11,comprising output signal analyzing means characterized by means fordistinguishing a first output signal time pattern, which is typical fora click movement, from a second output signal time pattern, which istypical for a scroll movement.
 18. An input device as claimed in claim17, characterized in that the output signal analyzing means comprisestorage and delaying means for combining measuring results obtained atdifferent time intervals.
 19. In input device as claimed in claim 11,characterized in that the measuring means are means for measuring avariation of the impedance of the laser cavity.
 20. An input device asclaimed in claim 11, characterized in that the measuring means is aradiation detector for measuring radiation emitted by the laser.
 21. Aninput device as claimed in claim 20, characterized in that the radiationdetector is arranged at the side of the laser cavity opposite the sidewhere the measuring beam is emitted.
 22. An input device as claimed inclaim 11, characterized in that it comprises an additional opticalsensor unit for measuring an additional movement in a directiondifferent from the directions of the scroll movement and of the clickmovement.
 23. A mobile phone apparatus comprising an input device asclaimed in claim
 11. 24. A cordless phone apparatus comprising an inputdevice as claimed in claim
 11. 25. A laptop computer comprising an inputdevice as claimed in claim
 11. 26. A hand-held computer comprising aninput device as claimed in claim
 11. 27. A write pen comprising an inputdevice as claimed in claim
 11. 28. A virtual pen comprising an inputdevice as claimed in claim
 11. 29. A keyboard for a desktop computerwherein an input device as claimed in claim 11 is integrated.
 30. Aremote control for a TV set, comprising an input apparatus as claimed inclaim 11.